The present invention relates to an apparatus for slow-speed reproduction of a moving picture signal, and more particularly, to an apparatus for constructing/reconstructing frames of a moving picture signal, recorded in an interlaced scanning mode, for slow-speed reproduction.
In apparatuses, such as TV sets, which display moving pictures, a frame is an elementary unit of the moving picture signal. In an interlaced scanning mode, each frame is composed of two fields. In case of a picture for NTSC, a time interval between two frames is one thirtieth of a second and a time interval between two fields is one sixtieth of a second. Therefore, field pictures having a constant interval of time are contained in each frame. In such a frame structure, frames in normal-speed reproduction are generated continuously by combining fields.
However, when reproducing at a low-speed, both fields of a single picture frame (for normal-speed reproduction) are repeatedly used for constructing sequential repetitive frames of a moving picture signal. Alternatively, either one of the two different fields is repeatedly used for constructing sequential repetitive frames of the moving picture signal. Problems with both types of frame construction will be described with reference to the graphs FIGS. 1 and 2.
In FIGS. 1 and 2, the horizontal axis represents a reproduction time and the vertical axis represents a recording time. Both FIGS. 1 and 2 describe a low-speed reproduction at a quarter speed.
FIG. 1 is a graph showing a slow-speed reproduction using a frame repetition method. The low-speed reproduction by the frame repetition method is performed in such a manner that a first field .largecircle. and a second field .diamond. of a first moving picture frame for normal-speed reproduction are repeatedly reproduced. Specifically, the same frame is repeatedly output in sequence four times, thereby realizing slow-speed reproduction at a quarter times speed.
FIG. 2 is a graph showing a slow-speed reproduction using a conventional field repetition method. First, either one of a first field or a second field of a first moving picture frame is selected. For example, when the first field of the first moving picture frame is selected, a first field and a second field of a second moving picture frame for low-speed reproduction are constructed with only the first field of the first moving picture frame. That is, a frame produced by one field, not a frame composed of two fields for normal-speed reproduction, is repeatedly output.
In the frame repetition method, two fields having a time difference are repeatedly used for reconstructing frames in the low-speed reproduction, and thus severe fluctuation is generated in an image exhibiting a large movement. In the field repetition method, loss of information in a remaining field, not used in frame construction, is experienced, and the time difference between reproduction frames becomes a time difference between two fields, resulting in unnatural movement.